Effective promotion of geopolymer concrete (GPC) is required to minimize the environmental threat caused by cement production as well as the disposal of fly ash (FA), ground granulated blast furnace slag (GGBFS), and other industrial wastes. To achieve this, a specific mix design procedure for the development of GPC is essential. One of the major challenges of GPC is a workable concrete of design strength with adequate initial setting time to allow for casting because GPC sets at a very short time after mixing (sometimes less than 7 min). There are currently two proposed mixed design procedures for GPC: the density method (BATCH A) and the water content method (BATCH B). This research investigated the suitability of both procedures for the design of GPC and their effect on the slump and compressive strength of GPC. A mix design of 40 MPa was done with both procedures employing low calcium fly ash (Class F FA) together with GGBFS as aluminosilicate precursor, sodium silicate, and sodium hydroxide at molarities of 8, 10, 12, 14, and 16, and alkaline activator solution at ratios of 2.5 and 1.5. Batch A design concrete got a maximum compressive strength of 65.7 MPa at a slump of 10 mm and an initial setting time of 6 min. Batch B design concrete proved to be a more suitable design procedure with a strength of 67.2 MPa, a slump of 180 mm, and an initial setting time of 19 min. The findings indicate that the water content method (Batch B) is more suitable for practical applications of GPC, as it ensures higher workability, adequate setting time, and comparable or superior strength.